Thermoplastic, also known as thermosoftening plastic, is a polymer that becomes pliable or moldable above a specific temperature, and returns to a solid state upon cooling. Most thermoplastics are polymers, and hence have high molecular weights. In the present invention, the thermoplastic polymers can have linear, branched, ladder, dendritic or other structures. The chains of such polymer thermoplastics associate through intermolecular forces. This property allows thermoplastics to be remolded because the intermolecular interactions spontaneously reform upon cooling. The thermoplastic polymers differ from thermosetting polymers (thermoset), which form irreversible chemical bonds between the polymer chains. And in case when such bonds break down, they will not reform again upon cooling.
Regarding thermoplastic polymers, within a temperature range above their respective glass transition temperatures and below their melting points, the physical properties of the thermoplastic polymers change drastically without associated phase changes. Within this temperature range, most thermoplastics are rubbery materials due to alternating rigid crystalline and elastic amorphous regions. Some thermoplastics do not fully crystallize above glass transition temperature, retaining some, or all of their amorphous characteristics.
Based on the type of the polymers that made the thermoplastic materials, various thermoplastic materials may have different properties and hence various applications. In addition, will the addition of various fillers, the properties of thermoplastic polymers can be significantly reinforced or altered. Various fillers can be added into the polymer matrix to form new polymer products. For example, some filler may be much cheaper than the polymer. Thus by using such filler, the manufacturing costs could be lowered. In addition, the addition of some filler may enhance certain valuable properties of the host polymer. Moreover, the addition of certain filler may even bring new properties to the host polymer.
Furthermore, sulfur, as an important additive, has been widely used in various polymer products, such as rubber, which is a thermosetting polymer. The process of vulcanization is the critical step for modern rubber production. Vulcanization is a chemical process for converting rubber or related polymers into more durable materials via the addition of sulfur. The vulcanized materials are less sticky and have superior mechanical properties. Hence the vulcanized rubber can be used for making tires, hoses, belts, etc. However, such rubber vulcanization is a very different process than the process of the present invention to make the disclosed composites. First, rubber is a thermosetting polymer that has very different response when heated. After being cured (hardened), the thermosetting polymer will not melt or perform deformation again. While the thermoplastic polymers disclosed in the present invention, when heated, will become soft and thus can be reprocessed many times by recycling. Second, in vulcanization, the added sulfur will perform chemical reaction to promote the formation of cross-links between the polymer chains. The cross-links introduced by vulcanization with sulfur prevent the polymer chains from moving independently. However, in the present invention, the added sulfur, as the filler, only physically fills the spaces within the polymer matrix. There is no chemical reaction occurs; and no cross-link has been formed following the addition of sulfur.
Moreover, sulfur has been reported to be added into the thermoplastic polymers, too. However, in that case, there is actually chemical reaction occurring. New chemical bond is formed, and certain properties of the thermoplastic polymers have been altered. Thus the final product is a new type of sulfur-rich poly-conjugated polymer. The newly gained properties may make the product suitable as electroactive or conducting materials.
Furthermore, the thermoplastic polymers can also be made into nanothermoplastic polymers. Nanocomposites are a group of multiphase solid material (matrix and filler), where one of the phases (usually the filler) has at least one dimension of nanoscale (less than 300 nanometers (nm)). In this way, the mechanical, electrical, thermal, optical, electrochemical and catalytic properties of the nanocomposite will differ markedly from those of the component materials. One easy way to make the polymer nanocomposite is appropriately adding nanoparticles to a polymer matrix. And this can enhance its performance, often dramatically, by simply capitalizing on the nature and properties of the nanoscale filler. The normal nanofillers used in this context are ceramics, clays, and certain carbon nanostructures, such as nanoplatelets or nanotubes.